diff --git a/pygit2.c b/pygit2.c
index 2b24ef8..e781744 100644
--- a/pygit2.c
+++ b/pygit2.c
@@ -310,7 +310,10 @@ py_str_to_git_oid(PyObject *py_str, git_oid *oid)
     return 0;
 }
 
-static PyObject*
+#define git_oid_to_python(oid) \
+        PyString_FromStringAndSize(oid.id, GIT_OID_RAWSZ)
+
+static PyObject *
 git_oid_to_py_str(const git_oid *oid)
 {
     char hex[GIT_OID_HEXSZ];
@@ -462,7 +465,7 @@ Repository_write(Repository *self, PyObject *args)
     if (err < 0)
         return Error_set_str(err, "failed to write data");
 
-    return git_oid_to_py_str(&oid);
+    return git_oid_to_python(oid);
 }
 
 static PyObject *
@@ -663,7 +666,7 @@ Repository_create_commit(Repository *self, PyObject *args)
     if (err < 0)
         return Error_set(err);
 
-    return git_oid_to_py_str(&oid);
+    return git_oid_to_python(oid);
 }
 
 static PyObject *
@@ -697,7 +700,7 @@ Repository_create_tag(Repository *self, PyObject *args)
     if (err < 0)
         return NULL;
 
-    return git_oid_to_py_str(&oid);
+    return git_oid_to_python(oid);
 }
 
 static PyObject *
@@ -1933,7 +1936,7 @@ Index_create_tree(Index *self)
     if (err < 0)
         return Error_set(err);
 
-    return git_oid_to_py_str(&oid);
+    return git_oid_to_python(oid);
 }
 
 static PyMethodDef Index_methods[] = {
diff --git a/test/test_index.py b/test/test_index.py
index 3c51792..6e73078 100644
--- a/test/test_index.py
+++ b/test/test_index.py
@@ -29,6 +29,7 @@
 
 from __future__ import absolute_import
 from __future__ import unicode_literals
+from binascii import b2a_hex
 import os
 import unittest
 
@@ -91,7 +92,8 @@ class IndexTest(utils.RepoTestCase):
         self.assertTrue('bye.txt' in index)
 
     def test_create_tree(self):
-        sha = self.repo.index.create_tree()
+        oid = self.repo.index.create_tree()
+        sha = b2a_hex(oid).decode('ascii')
         self.assertEqual(sha, 'fd937514cb799514d4b81bb24c5fcfeb6472b245')
 
     def test_iter(self):
diff --git a/test/test_repository.py b/test/test_repository.py
index 28f2011..56a401f 100644
--- a/test/test_repository.py
+++ b/test/test_repository.py
@@ -64,8 +64,9 @@ class RepositoryTest(utils.BareRepoTestCase):
         # invalid object type
         self.assertRaises(GitError, self.repo.write, GIT_OBJ_ANY, data)
 
-        hex_sha = self.repo.write(GIT_OBJ_BLOB, data)
-        self.assertEqual(len(hex_sha), 40)
+        oid = self.repo.write(GIT_OBJ_BLOB, data)
+        self.assertEqual(type(oid), bytes)
+        self.assertEqual(len(oid), 20)
 
     def test_contains(self):
         self.assertRaises(TypeError, lambda: 123 in self.repo)
@@ -117,8 +118,9 @@ class NewRepositoryTest(utils.NoRepoTestCase):
     def test_new_repo(self):
         repo = init_repository(self.temp_dir, False)
 
-        hex_sha = repo.write(GIT_OBJ_BLOB, "Test")
-        self.assertEqual(len(hex_sha), 40)
+        oid = repo.write(GIT_OBJ_BLOB, "Test")
+        self.assertEqual(type(oid), bytes)
+        self.assertEqual(len(oid), 20)
 
         assert os.path.exists(os.path.join(self._temp_dir, '.git'))